Method for producing hyperpure gallium



June 29, 1965 H. MERKEL METHOD FOR PRODUCING HYPERPURE GALLIUM Filed April 19. 1961 2 Sheets-Sheet l June 29, 1965 H. MERKEL 3,192,139

7 METHOD FOR PRODUCING HYBERPURE GALLIUM Filed April 19, 1961 I 2 Sheets-Sheet 2 Fig. 2

United States Patent Ofi ice 3,192,139 Patented June 29, 1965 3,192,139 IVIETHOD FOR PRODUCING HYPERPURE GALLIUM Hans Merkel, Eriangen, Germany, assignor to Siemens- Schuckertwerke Aktiengesellschaft, Berlin-Siemensstadt and Erlangen, Germany, a corporation of Germany Filed Apr. 19, 1961, Ser. No. 116,214 Claims priority, application Germany, Apr. 21, 1960,

6 Claims. (a. 204-64) purification of gallium. For example, it has been attempted to purify gallium metal by zone-pulling. The results are unsatisfactory. It is possible to purify gallium chloride GaCl by zone-pulling operations but the separation of gallium from the purified GaCl is difficult and not satisfactory for practical industrial application. This is mainly due to the fact that molten GaCl, is electrically nonconduc-tive. It is known to dissolve the purified compound in water, acid, or preferably in lyes, and to precipitate the metallic gallium electrolytically from the solution. This process, however, carries impurities from the solvent into the precipitated gallium. Further contamination is due to chemical attack upon the electrodes by the chlorine evolving at the anode; The electric current economy is relatively poor, and the electrolysis of aqueous gallium solutions takes place with violent liberation of gas at the electrodes.

It is therefore another, more specific object of my invention to provide a method for the production of hyperpure gallium which eliminates the above-mentioned difiiculties and deficiencies. According to the invention, I purify gallium by molten-bath electrolysis and use as an electrolyte a Ga(II)- halide previously subjected to extreme purificaton by zone-pulling in one or more passes.

The invention is based upon the observation that Ga (ID-halides are susceptible to extreme purification by zone-pulling. For example, GaBr can be purified in about 20 to 40 zone-pulling passes to such an extent that impurities are no longer discernible either spectroscopically or by the most sensitive known chemical methods of analysis. Molten Ga(II)-halides, in contrast to the trivalent gallium halides, are very good electric conductors. This is because Ga(II)-halides are ionic compounds of the type Ga'+(GaX having a monovalent gallium cation. The use of the Ga(ID-halides as the electrolyte for gallium purification by electrolysis of a molten or fused salt in accordance with my invention, is predicated upon the just-mentioned character of these compounds.

According to another feature of my invention, the above-described method is carried out in molten-salt electrolysis equipment whose electrodes consist of liquid gallium metal.

Examples of apparatus particularly well suitablefor performing the method according to the invention are FIG. 2 shows schematically another apparatus for two-stage processing; and

FIG. 3 is a single-stage apparatus according to the invention for large-quantity production of gallium.

The apparatus according to FIG. 1 comprises a vessel 1 for accomodating the electrolyte. The vessel 1 is mounted in a furnace schematically shown at 2 and consisting for example of an electric-resistance furnace. The electrode portions of the vessel are designed as U- shaped tubes, the anode tube is denoted by 3 and the cathode tube by 4. The current-supply conductors 5 and 6 are provided with small platinum tips 5a and 6a, for example of 0.3 mm. diameter, through which the current passes from the conductor to the liquid electrodes. The vessel portions 3, 1 and 4 are sealed by conical, ground closure caps 7, 8 and 9 respectively.

In performing the method of the invention, anode tube 3 is filled with impure gallium whereas the cathode tube 4 is filled with gallium of highest available purity, for example gallium already pre-purified by known purification methods.

It is preferable to use pre-purified gallium metal also in the anode tube rather than impure gallium as mentioned above. Particularly suitable for this purpose is gallium metal pre-purified in accordance with the method described in US. Patent 2,927,853. According to this method, the gallium metal, in form of droplets, is exposed, at a temperature between about 400 to about 1200 C., to a flow of'nitrogen or ammonia gas.

The main vessel portion 1 is filled with the Ga(II)- halide electrolyte, for example GaBr previously extremely purified by zone-pulling, the electrolyte forms an interface with the gallium electrodes. The electrolyte can be produced in known manner, for example by heating of commercially available gallium metal in a flow of nitrogen laden with bromine vapor. The result ing GaBr converts into GaBr by additional metallic gallium. The resulting GaBr can be rendered hyperpure, i.e. spectroscopically pure, by zone-pulling in about 20 to 40 zone passes.

The vessel portion 1 is heated to a temperature of approximately C. by heating means 2. The electrolysis is preferably performed at a current density of 5 to 10 a./dm. (amps per square decimeter). This results in the terminal voltage of 0.5 to 1 v. in apparatus accord ing to FIG. 1. Metals, e.g. silver, copper, lead, etc., that are nobler than gallium and contained therein remain unchanged in the anode portion. Due to thei high rate of diffusion, these nobler metals distribute themselves very rapidly throughout the entire quantity of the anode gallium, so that even after prolonged duration of the electrolysis, enrichment in these impurities does not occur in the vicinity of the anode surface. Although less noble metals, e.g. aluminum and zinc, enter anodically into solution along with gallium, only pure gallium is precipitated at the cathode. While'the precipitation potentials of the particular metals is a factor, the high refining action is predominantly a consequence of the fact that the base metals enter into the anion complex of the electrolyte and therefore do not disturb the precipitation of pure gallium at the cathode. Thus, for example, anodically dissolved aluminum forms the negatively charged complexion (AlBr The quantitative analysis of the electrolysis shows that Faradays law is strictly satisfied. That is, exactly 1 mole of gallium is converted by a quantity of electricity in the amount of 96,500 coulombs. This permits the conclusion that the electrolytic phenomena are determined 'by the electric charging, migration, and discharging of mono-valent Ga-cations. This is in' harmony with the formulation of the Ga(II)-halides as being gallium(I)- 3 tetrahalogallates (HI), i.e. Ga+(GaX as ascertained in a different way and published recently. See Partington, Textbook of Organic Chemistry, 6th edition (Macmillan and Co., London), page 816.

In conjunction With the production method of my invention, this result is of outstanding economical importance because the molten-salt electrolysis of the Ga(11)- halides yields the electrochemically possible maximum quantity of gallium,namely 2.6 g. Ga/ah. (grams of gallium per ampere hour). This quantity is exactly twice as large as would have to be expected on the basis ofthe simple formula GaX with bi-valent Ga++ cations.

Also economically important is the fact that with fusedbath (molten-salt) electrolysis, the refined gallium obtained utilizes 100% of the electric current. This is because the electric energy supplied to the system cannot be consumed by undesired secondary reactions, for example, gas development at the electrodes. This absence of gassing also permits performing the electrolysis in enclosed apparatus, thereby excluding the danger of contamination by atmospheric impurities.

The electrolysis equipment according to FIG. 1, suit able for producing relatively small gallium quantities up to about 50 g. Ga/ 24- hours, is preferably so dimensioned that the cathode space 4 is just filled with gallium at the termination of the 24-hour operating period. To with draw the purified gallium, cap 9 is removed and the quantity of gallium metal equivalent to the gallium precipitated is withdrawn from the cathode space. 4 by means of a pipette. The same quantity of impure gallium is added to the anode space 3.

Example 1 fication can be improved by performing the process in a plurality of steps, as already mentioned above. The embodiment of equipment shown in FIG. 2 is suitable for this purpose. The design of the individual stages essentially corresponds to the single-stage design according to FIG. 1. Shown between the two stages is an auxiliary electrode in a vessel portion 20. This auxiliary electrode makes it possible, in cooperation with the respective current sources provided for the two stages and in conjunction with an adjustable resistor, to control and regulate the current and voltage conditions of each individual cell independently of the other. However, the auxiliary electrode is dispensable for normal operation of the plant if so desired.

The apparatus according to FIG. 2 comprises an anode vessel 11, a cathode vessel 12, two vessel portion 13 and 14 for accommodating the electrolyte, and live ground covering caps 15, 16, 1'7, 18, 19, for vacuum-tightly closing and sealing the above-mentioned four vessel portions and the vessel portion in which the auxiliary electrode is located. The current supply conductors 21, 22 and 23 are provided with small platinum tips for transferring the current to the respective gallium quantities. The current sources 24 and 25 for the two respective stages are connected in series with adjustable resistors 26 and 27 respectively. Each of the two circuits also comprises an ammeter 28 or 29, and a voltmeter 30 or 31.

The performance of the two-stage apparatus, in principle, is as described above with reference to the apparatus of FIG. 1. The purified gallium precipitated at the cathode side of the first stage constitutes the anode side of the second stage in which the gallium is further purified and is precipitated at the cathode side of the second stage. In an analogous manner, the apparatus may be provided with any desired number of further stages.

Example 2 Commercial gallium and an electrolyte consisting of GaBr were used in the apparatus of FIG. 2. .Both materials were prepurified as mentioned in Example 1. The anode surface per cell was 7 cm. The cathode surface per cell was 1.75 cm}. At a voltage of 0.5 v. at the one cell and 0.9 v. at the other cell, an electrolysis current of 0.7 amp. adjusted itself. The two vessels with the electrolyte were kept at a temperature of C. The yield of 43.5 g. was obtained for 24 hours. Since in this example a two-stage purification was performed, the gallium produced was of even higher purity than the material of Example 1.

For producing large quantities of hyperpure gallium, it is necessary to provide electrolysis equipment that affords accommodating the largest feasible anode surface so that, for example, at anode-currentdensities between 5 and 10 a./dm. correspondingly increased gallium throughputs are afforded at voltages between 0.5 to 1 v. In this case it is preferable to connect to the anode side of the electrolysis cell a gallium supply container with a level regulator, and to provide the cathode side with a collector vessel into which the purified gallium can drip continuously. For producing approximately 1 kg. refined gallium within 24 hours, an anode surface of approximately 1.6 din. is needed. The cathode surface is preferably smaller than the anode surface subdivided into several areas to obtain a favorable course of the current paths.

An example of such a design for large-scale production of gallium is illustrated in FIG. 3. The anode gallium and the electrolyte are located in an electrolytic cell 32. The cathode comprises two portions 33and 34 which communicate with the cell 32 and with an end portion 36 of the cathode. The anode area is greater than the cathode area. Thecurrent supply can be' effected for example by platinum tips that are fused into the vessel walls, such tips being indicated at 37 and 38. Located on the anode side of the apparatus is a gallium storage vessel 39 with a syphon tube 40 and a level regulator 41, the inlet openingis covered by a cap 42. The end portion 36 of the cathode is sealed by the ground cap 43 and provided with an overflow nipple 44. The cathodically precipitated gallium collects in a collector vessel 45 which is closed by sealing cap 46 which contains an air filter 47. The level regulator 41 permits adjusting the height of the anode gallium in the electrolytic cell and maintaining it constant. The cell 32 is located within an electric furnace whose heater winding is denoted by 48.

For the production of relatively small and medium throughputs of gallium, the electrolytic apparatus according to the invention are preferably made of glass or quartzglass.

For larger throughputs, for example. in equipment according to FIG. 3, recently developed quart z-glass-like materials which are particularly designed for larger dimensions can be used. This material is produced by a sintering or similar ceramic method and is commercially avail able under the trade name Rotosil.

This material readily affords designing electrolytic cells, for example for 0.4 times 2 m.:0.8 m. anode surface which furnish 50 kg. hyperpure gallium metal within 24 hours at 1 volt cell voltage and 800 a., thus requiring less than 20 kwh. expenditure in electrical energy.

GaCl G312 can be used in lieu of GaBr in the same manner as that described above for GaBr When using Gacl the fact that an abrupt volume change takes place when the melting zone solidifies, must be taken into consideration When dimensioning the melting vessel.

The method according to the invention affords the production of gallium metal which is purer than 99.99999%. The known trace analysis methods (Dithizon method,

lium(II)-halide being pre-purified by zone-pulling and using liquid gallium metal as electrodes.

2. The method of producing hyperpure gallium by electrolysis of a fused bath of electrolyte which comprises using gallium(II)-bromide, GaB1' as said electrolyte, said gallium(II)-bromide being pre-purified by zone-pulling and using liquid gallium metal as electrodes.

3. The method of producing hyperpure gallium by electrolysis of a fused bath of electrolyte which comprises using pre-purified gallium(II)-bromide as said electrolyte and liquid gallium metal as electrodes, said liquid gallium metal being pre-purified, at a temperature between about 400 C. and about 1200 C., by exposure, in the form of droplets, to a flow of nitrogen-containing gas.

4. The method of producing hyperpure gallium by electrolysis, which comprises zone-pulling gallium(II)-halides of the group consisting of chlorine, bromine and iodine to pre-purify said gallium(II)-halide, using said pre-purified gallium(II)-halide as a fused electrolyte for said electrolysis and liquid gallium metal as electrodes.

5. The method of producing hyperpure gallium by electrolysis of a fused bath of electrolyte which comprises using monovalent gallium cations extremely pre-purified by Zone-pulling and liquid gallium metal electrodes.

6. The method of producing hyperpure gallium by electrolysis of a fused bath of electrolyte which comprises using monovalent gallium compounds of the group consisting of Ga[AlBr and Ga[AlCl as said electrolyte, said gallium compounds being pre-purified by zone-pulling and liquid gallium metal electrodes.

References Cited by the Examiner UNITED STATES PATENTS 1,842,254 1/32 Driggs 204-64 2,5 00,284 3 5 0 Heyrovsky 204-219 2,927,853 3/60 Merkel 7584 2,991,235 7/61 Ravier 20464 FOREIGN PATENTS 72,710 1 Sweden.

OTHER REFERENCES Jahresbericht Uber Die Fortschritte der Chemie, Theil 1 (1888).

JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, WINSTON A. DOUGLAS,

Examiners. 

1. THE METHOD OF PRODUCING HYPERPURE GALLIUM BY ELECTROYSIS OF A FUSED BATH OF ELECTROYTE WHICH COMPRISES USING GALLIUM (II) HALIDES OF THE GROUP CONSISTING OF CHLORINE, BROMINE AND IODINE AS SAID ELECTROLYTE, SAID GALLIUM (II)-HALIDE BEING PRE-PURIFIED BY ZONE-PULLING AND USING LIQUID GALLIUM METAL AS ELECTRODES. 